Powder metal material
The powder metal process begins with a premixed powder of the required alloying elements as well as a lubricant. The aPriori baseline powder metal model assumes the powders are premixed. The baseline material costs include both the raw material and mixing costing.
Note If you want to cost the mixing process as a separate step in the routing, this option can be configured into a customer-specific VPE.
Powder metal is unique compared to other manufacturing processes because it supports the ability to design a material to fit very specific material property requirements. This in turn has allowed for a very significant amount of different metal alloys to be created. A list of publicly known materials used in the powder metal process is maintained by the Metal Powder Industry Federation (MPIF) in their publication of the Standard 35. This document is rich with material data and can be obtained through the MPIF.
Note Standard 35 does not list the required compaction curve information necessary for the model, so it must be calculated when adding materials to a VPE.
The aPriori baseline Powder Metal cost model has the following material properties in the material table:
• Material Name
• Material Description – Free form description of the material.
• Material Type – Material type drives the cut code. aPriori Support can point you to cut codes by material type and this information is available on the web.
• Cut Code – The cut code is used by the cycle time calculation in secondary machining processes.
• Unit Cost ($/kg) – The cost per kilogram paid for the raw material.
• Green Density (kg/m3) – The green density of the part is the density of a part when it is pressed. At that time, the part is in its “green” state. No metallurgical bonds have been formed and the part is holds its shape only as a result of the compaction. The parts can be easily cracked or broken by hand at this stage. In the powder metal process, this green density is typically in the range of 6.9g/cm3 for ferrous metals, however that is not a constant. The user will have the ability to change the green density of the part through a process setup option. Picking different green densities will result in a change in the required compaction pressure needed to compress the part to that specific density. The relationship between the green density and the compaction pressure will follow the compaction curve typically in the shape of a parabola. The resulting polynomial expression for the compaction curve is ultimately what drives the machine selection and the material cost per part.
• Apparent Density (kg/m3) – The apparent density of the material is the density of the raw material prior to compaction.
• Coef A – CoefA, Coef B, and Coef C are the coefficients of the compaction curve, which are used to determine the force required to press the powder to the required density. aPriori has a methodology for calculating the coefficients, which you can get from support, if you are looking to add materials into your specific VPE.
• Coef B – for the compaction curve, see explanation under CoefA.
• Coef C – for the compaction curve, see explanation under CoefA.